Characteristics of metabolism and function of the neural retina (NR) and pigment epithelium (PE) are studied in culture cells and in freshly dissected tissue. l. Several new neurotransmitter/neuromodulator receptors have been identified and partially characterized in retina, pigment epithelial cells, and retinoblastoma cells in culture. These include receptors for vasoactive intestinal peptide, glucagon prostaglandin El, histamine, and isoproterenol. These all operate through activation of adenylate cyclase activity. 2. Human retinoblastoma cells can be induced to differentiate in culture. Agents such as cyclic AMP, butyrate, and retinoic acid can be used to induce differentiation, stop growth, and cause cell death. 3. GABA, besides being a classical neurotransmitter, appears to exert a marked trophic influence on early retinal development.